.SYA' WILLIAM SIEMENS, F.R.S. 



207 



\vhrii little reliable information existed on the subject, that the 

 electric liirht at Dnngcness lost its brilliancy in a more rapid ratio 

 than the oil light with which it was put into juxtaposition. He 

 had attempted to find an explanation in the fact of the electric 

 MLrlit Ix-ing of a more refrangible character than the oil light, so 

 that in meeting with any obstructing medium it would suffer 

 . ai nl would more rapidly be brought down to a common level 

 with the other light ; and he had held that, in order to get more 

 penetrating power, not intensity alone, but intensity with quantity, 

 as represented by large surface, would be required. The electric 

 light then exhibited had a dioptric lantern only 30 centimetres 

 (1 foot) diameter ; and it seemed reasonable that, with that 

 illuminated surface, although the light might be an intense one, 

 no distant effect through an obscuring medium could be effected. 

 Moreover, the electric lamps of that day were not very perfectly 

 iviMilated, and it was probable that the focus of that lamp 

 fluctuated considerably. The results mentioned in the paper 

 bore out, he thought, the views he had then expressed. At 

 Dungeness the oil lamp had a power of 250 candles, and the 

 electric light a power of G70 candles. Whatever standard was 

 employed, he presumed it was the same for both lights. The 

 proportion was only that of 2| to 1, and the disadvantage in the 

 case of the electric light was that it had a smaller lamp. At La 

 He" ve, Dr. Barnard ascertained that the oil lamp was nearly equal 

 in penetrating power to the electric light, although the latter had 

 about six times greater intensity again showing a relative ad- 

 vantage in favour of the oil lamp. At the Lizard, the electric 

 light had a penetrating power to double the distance of the oil 

 lamp. In that case a large dioptric apparatus was employed, 

 and the circumstances, or conditions, which he had formerly 

 contended for had been realised. The electric light was not 

 presented as a point, but as an illuminated surface. It was said 

 by those who advocated oil in preference to electricity, that if an 

 oil lamp, as Mr. Vernon-Harcourt had put it, of 3,000 candle- 

 power were substituted, the same penetrating power would be 

 obtained, and that with 5,000 candles the power would be greater ; 

 but Mr. Vernon-Harcourt had not explained how he would get 

 that amount of light into the focus. It was true that Mr. Wigham 

 had said he liked his light ex-focal, in order to give a glare ; but 



